Palladium dimethylglyoxime

Dimethylglyoxime reagent yellow, crystalline precipitate of palladium dimethylglyoxime, Pd(C4H702N2)2, insoluble in m hydrochloric acid (difference from nickel and from other platinum metals) but soluble in dilute ammonia solution and in potassium cyanide solution (cf. Nickel, Section III.27, reaction 8). 

A useful spot test utilizes the fact that a suspension of red nickel dimethylglyoxime in water when treated with a neutral or acetic acid solution of a palladium salt yields the yellow palladium dimethylglyoxime, which is sparingly soluble in dilute acids. The test is best performed with dimethylglyoxime paper the latter is prepared as follows. Immerse drop-reaction paper in a 1 per cent alcoholic solution of dimethylglyoxime, dry, then immerse again in a solution of 05m nickel chloride rendered barely ammoniacal. The nickel complex precipitates wash thoroughly with water, immerse in alcohol and dry. 

Place a drop of the neutral or acetic acid test solution upon nickel dimethylglyoxime paper, and almost dry by waving over a flame. Immerse the paper in dilute hydrochloric acid until the surface surrounding the fleck becomes white, and then wash the paper with cold water. A pink to red spot remains, depending upon the quantity of palladium present. The acid-stable palladium dimethylglyoxime at the site of the fleck protects the underlying red nickel dimethylglyoxime from attack by the acid. 

The precipitation of palladium dimethylglyoximate from an acid medium is an excellent separation method. In the separation of microgram quantities of Pd, nickel has been used as a collector [12]. The optimum pH for the precipitation is 6.5 (acetate medium). If Au(III) is separated beforehand by reduction with oxalic acid, and if copper is masked with EDTA, the separation of traces of palladium (with Ni as collector) is specific. 

Separation of Pd with a collector. To the sample solution (-100 ml) in 0.1 M HCl, containing not more than 50 pg of Pd and heated to 80°C, add a macerated filter paper and 1 ml of 5% oxalic acid solution. Keep the solution at 80°C for 1 h, then allow it to cool. Filter off the precipitate of elemental gold and silver chloride together with the paper. To the filtrate add successively 2 mg of nickel (as its sulphate solution), 2 ml of 20% potassium sodium tartrate solution [to mask Fe(IIl), Al, Ti, etc.], 2 g of sodium acetate, 1 ml of 0.1 A/ EDTA, and 2 ml of the H2Dm solution (pH -6.5). After 30 min, filter off the precipitate of nickel- and palladium dimethylglyoximates. Wash the precipitate from the filter paper into a beaker, add 1 ml of cone. HCl, and evaporate to 5-10 ml, depending on the quantity of Pd in the solution. 

Bright yellow inner complex palladium dimethylglyoxime (I) is not soluble in acids but it dissolves in alkali hydroxides. The yellow solution contains alkali palladium dimethylglyoxime (II), in which the palladium is a constituent of an inner complex anion. 

Procedure. A drop of the alkaline test solution and a drop of alkali palladium dimethylglyoxime are brought together on a spot plate a drop of nickel-ammonium solution is then introduced. A red precipitate or pink coloration appears, the shade depending on the amount of alkali cyanide present. A blank test is necessary only when small quantities of cyanide are suspected. 

Reagents 1) Alkali palladium dimethylglyoxime Purest Pd-dimethyl-glyoxime (prepared by precipitation of an acid solution of PdClg with dimethylglyoxime and thoroughly washed) is shaken with 3 N potassium hydroxide. The undissolved portion is filtered off. 

The addition of potassium iodide, which forms insoluble Pdlg, completely inhibits the catalytic acceleration of the nickel reduction. A saturated water solution of Pdia has no action, in contrast to a saturated solution of palladium dimethylglyoxime, where one drop has a distinct effect. 

The palladium content of a steel sample was determined as follows. A 16.312 g steel sample was dissolved in concentrated HCl(aq). The solution obtained was treated to remove interfering ions, to establish the proper pH, and to obtain a final solution volume of 250.0 mL. A 10.00 mL sample of this solution was then treated with dimethylglyoxime to convert all of the palladium to palladium dimethylglyoximate, a chemical compound that is 31.61% Pd (by mass), 28.54% C, 4.19% H, 19.01% O, and 16.64% N. The mass of purified, dry palladium dimethylglyoximate obtained was 0.0784 g. 

This reagent, to which the name nioxime has been given, ia employed for the determination of palladium and may also be used for nickel it is soluble in water, and possesses advantages over dimethylglyoxime. The latter is used as a solution in alcohol and may therefore contaminate the palladium or nickel precipitate when added to an aqueous solution. 

Dimethylglyoxime. The complexes with nickel and with palladium are soluble in chloroform. The optimum pH range for extraction of the nickel complex is 4-12 in the presence of tartrate and 7-12 in the presence of citrate (solubility 35-50 fig Ni mL 1 at room temperature) if the amount of cobalt exceeds 5 mg some cobalt may be extracted from alkaline solution. Palladium(II) may be extracted out of ca lM-sulphuric acid solution. 

Cyclohexane-1,2-dione dioxime (nioxime) (IV) is more soluble in water (8.2 g L 1 at 21 °C) than is dimethylglyoxime it is an excellent reagent for the gravimetric determination of palladium. 

Determination of palladium with dimethylglyoxime Discussion. This is one of the best methods for the determination of the element. Gold must be absent, for it precipitates as the metal even from cold solutions. The platinum metals do not, in general, interfere but moderate amounts of platinum may cause a little contamination of the precipitate, and with large amounts a second precipitation is desirable. The precipitate is decomposed by digestion on the water bath with a little aqua regia, and diluted with an equal volume of... 

An objection to the precipitation of palladium with dimethylglyoxime is the voluminous character of the precipitate. Hence if much palladium is present, an aliquot part of the solution should be used. 

Palladium, D. of as dimethylglyoximate. (g) 463 as nioximate, (g) 474 by EDTA, (ti) 329 Paper chromatography 229 see Thin layer chromatography Parallax errors due to, 85 Parallel determinations 132 Partial ionic equations 850, (T) 851 Partition chromatography 13. 217 Partition coefficient 162 Patton and Reeder s indicator 317, 328 Peptisation 419. 421... 

The reaction of aqneons green Np, or its bine ammonia complex, with colorless dimethylglyoxime (DMG) to form a vibrantly red precipitate of a 1 2 metaLDMG complex demonstrates an example of precise stereochemistry and oxime deprotonation in what is perhaps the archetypal analytical metal dioxime reaction (equation 1). This transformation certainly intrigued both authors early in their education. It is interesting to note that DMG is an excellent example of highly specific reagent because under the same reaction conditions only yellow palladium chelate is also precipitated. 

It has been mentioned that the dimethylglyoxime complexes of nickel, palladium, and platinum, and the N-methylsalicylaldimine complexes of... 

Palladium compounds have also been reported to stabilize unexposed areas to heat.199 The compounds disclosed include the complexes of triphenylphosphine, bipyridine, acetylacetone and dimethylglyoxime. Preferred compounds appear to be the acac analogs. 

Z)-A3-Alkenyl sulfones. The 7r-allylpalladium complexes of 1,3-dienes react with sodium neophylsulflnate to give a palladium complex which on treatment with dimethylglyoxime gives (Z)-sulfones with high regio- and stereoselectivity.3 Example ... 

Separation. Palladium is precipitated in Group II as PdS it is insoluble in ammonium polysulphide solution and therefore accompanies the elements of Group IIA. It is ultimately identified in acid solution as the dimethylglyoxime complex. 

Tokalioglu, S., Oymak, T., Kartal, S. Determination of palladium in various samples by atomic absorption spectrometry after preconcentration with dimethylglyoxime on silica gel. Anal. Chim. Acta 511, 255-260 (2004)... 

Dimethylglyoxime has long been used as a precipitant for nickel and palladium. Nickel is usually precipitated from an ammoniacal tartrate buffer of pH about 8. Under these conditions iron and many other metals, even in large amounts, do not interfere. Palladium is precipitated from hydrochloric or sulfuric acid solution. Nioxime ° (1,2-cyclohexanedionedioxime) has the advantage of being more soluble in water than dimethylglyoxime and therefore less subject to coprecipitation with the metal chelate. 

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